Ss. Barsanuphius and John ca. 6th cent.
Q: When I pray or occupy myself with psalmody, and I do not feel the power of the words I pronounce, by reason of the insensitivity of the heart; then what profit is there for me from this prayer?
A: Even though you do not feel the power of what you pronounce, still the demons feel it, hear and tremble. And so, do not cease to occupy yourself with psalmody and prayer, and little by little, by God’s help, your insensitivity will be turned to softness. (Answers to Questions of Disciples, 718)